Why they'd do this I'm not sure. If they were religious they may have entrenched opinions, built upon firm stereotypes from their own parents. They now face detailed examination, probably for the very first time. Yes, they should be affirming but they're struggling to cope with this currently. Heck I was.
Parents often go into a denial phase - "it can't have happened" or "if I ignore it it'll go back to 'normal'." I have had it described to me as 'grief' - the loss of a child. I'm so grateful that a group were able to support me and allow me to understand what I needed to do... without telling me that I had failed. It's painful BUT out of loss comes new birth, a new chapter. When that parent comes out of the grief process eventually (it may not take a day or so...) they're searching for answers. They may try to reconnect with their child. Support them please. I love the expression their rainbow child. A new dawn, a new emergence of that father-child love but it is a process and one that will develop, ever deeper over weeks, months, years.
Please rather than criticise the parents over their reaction, support them as you'd support their child.
Let's bring families back together.